1. Fungi
Chapter 31

2. Defining Fungi
Mycologists believe there may be as many as 1.5 million fungal species
Single-celled or multicellular
Sexual or asexual
Specialized to extract and absorb nutrients from surroundings
Animal and fungi last shared a common ancestor 460 MYA
Some debate on timing

3. 7 monophyletic phyla Microsporidia Blastocladiomycota
Neocallismastigamycota
Chytridiomycota
Glomeromycota
Basidiomycota
Ascomycota

4. Neocallimastigomycota Chytridiomycota Glomeromycota Basidiomycota
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Microsporidia
Blastocladiomycota
Zygomycota
Neocallimastigomycota
Chytridiomycota
Glomeromycota
Basidiomycota
Ascomycota
10 µm
520 µm
333 µm
312 µm
160 µm
300 µm
Dikarya
Fungi
a: © Dr. Ronny Larsson; b: Contributed by Don Barr, Mycological Society of America; c: © Carolina Biological Supply Company/Phototake; d: Contributed by Don Barr, Mycological Society of America; e: © Dr. Yuuji Tsukii; f: © Yolande Dalpe, Agriculture and Agri-Food Canada; g:© inga spence/Alamy; h: © Michael&Patricia Fogden

6. General Biology of the Fungi
Multicellular fungi consist of long, slender filaments called hyphae
Some hyphae are continuous
Others are divided by septa
Cytoplasm flows throughout hyphae
Allows rapid growth under good conditions

7. (right): © Garry T. Cole/ Biological Photo Service
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dikaryotic
cell
Septa with
pores
Nuclei
Nuclei
Hypha
Pore
Septum
0.2 µm
(right): © Garry T. Cole/ Biological Photo Service

8. Mycelium – mass of connected hyphae Fungal cell walls include chitin
Grows through and digests its substrate
Fungal cell walls include chitin
Also found in the hard shells (exoskeletons) of arthropods

9. Hyphae may have more than one nucleus
Monokaryotic – 1 nucleus
Dikaryotic – 2 nuclei
Both genomes transcribed
Sometimes many nuclei intermingle in the common cytoplasm of the fungal mycelium
Heterokaryotic – nuclei from genetically distinct individuals
Homokaryotic – nuclei are genetically similar to one another

10. Fungi have an unusual mitosis
Cell is not relevant unit of reproduction
Nuclear envelope does not break down and re-form
Instead, the spindle apparatus is formed within it
Fungi lack centrioles
Spindle plaques regulate microtubule formation during mitosis

11. Reproduction Capable of both sexual and asexual reproduction
Fusion of two haploid hyphae of compatible mating types
In some fungi, fusion immediately results in a diploid (2n) cell
Others, have a dikaryon stage (1n + 1n) before parental nuclei form diploid nucleus
May form mushrooms or puffballs

12. Spores are the most common means of reproduction among fungi
May form from sexual or asexual processes
Most are dispersed by wind

13. a: © Carolina Biological Supply Company/Phototake
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Young
gametophyte (n)
Female gametangium
Male gametangium
MITOSIS
Haploid gametes (n)
Gametophyte (n)
Mature
gametophyte (n) n
Haploid
zoospore (n)
FERTILIZATION 2n
Sporangium (2n)
Sporophyte(2n)
MEIOSIS
Young
sporophyte (2n)
Diploid
zoospores (2n)
Asexual sporangium
Asexual
reproduction
Sporophyte
Mature sporophyte (2n)
Young sporophyte (2n) a. b.
100 µm
a: © Carolina Biological Supply Company/Phototake

14. Sexual Reproduction Plasmogamy- Union of cytoplasm of two hyphae
Karyogamy- Fusion of 2 nuclei to form a diploid zygote

15. Asexual reproduction more common
Fusion of gametangia
Haploid nuclei fuse to form diploid zygote nuclei – karyogamy
Develops into zygosporangium in which zygospore develops
Meiosis occurs during germination of zygospore
Releases haploid spores
Asexual reproduction more common
Sporangiophores have sporangia that release spores

16. Spore germination leads to the production of monokaryotic hyphae
Results in a monokaryotic mycelium, or primary mycelium
Different mating types of monokaryotic hyphae may fuse
Results in a dikaryotic mycelium, or secondary mycelium
Heterokaryotic mycelium
Basidiocarps (mushrooms) are formed entirely of secondary mycelium

17. Asexual Reproduction
Budding
Fragmentation
Binary fission
Sporulation

18. Nutrition Obtain food by secreting digestive enzymes into surroundings
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nutrition
Fungal
loop
Fungus
Nematode a.
370 µm
© Carolina Biological Supply Company/Phototake b.
© L. West/ Photo Researchers, Inc.
Obtain food by secreting digestive enzymes into surroundings
Then absorb the organic molecules produced by this external digestion
Great surface area-to-volume ratio
Fungi can break down cellulose and lignin
Decompose wood
Some fungi are carnivorous

19. Glomeromycota Glomeromycetes are a tiny group of fungi
Form intracellular associations with plant roots called arbuscular mycorrhizae
Cannot survive in absence of host plant
No evidence of sexual reproduction
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Neocallimastigomycota
Blastocladiomycota
Chytridiomycota
Glomeromycota
Microsporidia
Basidiomycota
Zygomycota
Ascomycota
Fungi

20. Basidiomycota Basidiomycetes are some of the most familiar fungi
Mushrooms, toadstools, puffballs, shelf fungi, etc.
Also important plant pathogens like rusts and smuts
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Neocallimastigomycota
Blastocladiomycota
Chytridiomycota
Microsporidia
Glomeromycota
Zygomycota
Basidiomycota
Ascomycota
Fungi

21. Ascomycota Contain about 75% of the known fungi
Includes bread yeasts, common molds, cup fungi, truffles, and morels
Serious plant pathogens – cause of chestnut blight and Dutch elm disease
Penicillin-producing fungi are in the genus Penicillium
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Neocallimastigomycota
Blastocladiomycota
Chytridiomycota
Microsporidia
Glomeromycota
Basidiomycota
Zygomycota
Ascomycota
Fungi

22. Yeast Unicellular ascomycetes Most reproduce asexually by budding
Yeasts can ferment carbohydrates
Break down glucose into ethanol and CO2
Used to make bread, beer, and wine
Saccharomyces cerevisiae

23. Yeast is a long-standing model system for genetic research
First eukaryotes to be manipulated extensively
Saccharomyces cerevisiae first eukaryote to have genome sequenced
Yeast two-hybrid system has been an important component of research on protein interactions

24. Ecology of Fungi
Fungi, together with bacteria, are the principal decomposers in the biosphere
Break down cellulose and lignin from wood
Release carbon, nitrogen, and phosphorus

25. Fungi symbioses Interactions
Obligate symbiosis – essential for fungus survival
Facultative symbiosis – nonessential
Interactions
Pathogen – pathogens harm host by causing disease
Parasites cause harm to host (do not cause disease)
Commensal relationships benefit one partner but does not harm the other
Mutualistic relationships benefit both partners

26. Endophytic fungi Live in the intercellular spaces inside plants
Some parasitic, some commensalistic
Some fungi protect their hosts from herbivores by producing toxins

27. Lichens
Symbiotic associations between a fungus and a photosynthetic partner
Cyanobacteria, green algae, or sometimes both
Most are mutualistic
Ascomycetes are found in all but about 20 of the 15,000 lichen species

28. Fungi protect their partners from strong light and desiccation
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Fungal
loop
Fungus
Nematode a. b.
370 µm
a: © Carolina Biological Supply Company/Phototake; b: © L. West/ Photo Researchers, Inc.
Fungi in lichens are unable to grow normally without their photosynthetic partners
Fungi protect their partners from strong light and desiccation
Lichens have invaded the harshest habitats
Striking colors play a role in protecting photosynthetic partner
Sensitive to pollutants

29. Mycorrhizae Mutualistic relationships between fungi and plants
Found on the roots of about 90% of all known vascular plant species
Function as extensions of root system
Increase soil contact and absorption
Two principal types
Arbuscular mycorrhizae
Ectomycorrhizae

30. Arbuscular mycorrhizae
By far the most common
Fungal partners are glomeromycetes
No aboveground fruiting structures
Potentially capable of increasing crop yields with lower phosphate and energy inputs
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Arbuscular Mycorrhizae
Root
3.7 µm a.
© Eye of Science/Photo Researchers, Inc.
Hyphae penetrate the root cell wall but not plant membranes

31. Ectomycorrhizae Most hosts are forest trees (pines, oaks)
Fungal partners are mostly basidiomycetes
At least 5000 species of fungi are involved in ectomycorrhizal relationships
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Ectomycorrhizae
50 µm b.
© Dr. Gerald Van Dyke/Visuals Unlimited
Hyphae surround but do not penetrate the root cells

32. Animal mutual symbioses
Ruminant animals host neocallimastigamycete fungi in their gut
Leaf-cutter ants have domesticated fungi which they keep in underground gardens
Ants provide fungi with leaves
Fungi are food for the ants

33. Fungal Parasites and Pathogens
Fungal species cause many diseases in plants
Among most harmful pests of living plants
Can also spoil harvested or stored food products

35. Fungi may secrete substances making food unpalatable, carcinogenic, or poisonous
Fusarium – vomitoxin
Aspergillus flavus – aflatoxin

36. Fungi also cause human and animal diseases
Candida – thrush; vaginal infections
Pneumocystis jiroveci – pneumonia in AIDS
Athlete’s foot, ringworm, and nail fungus
Fungal diseases are difficult to treat because of the close phylogenetic relationship between fungi and animals

37. Batrachochytrium dendrobatidis causes chytridiomycosis
– Responsible for the worldwide decline in amphibian populations